Manufacture of cellulose and the like



April 10, 1934.

A. LEMBERGERET AL MANUFACTURE OF CELLULOSE AND LIKE Filed Feb. 17, 1951 lNve f',

Flmbe ev* I Patented Apr. 10, 1934 PATENT OFFICE MANUFACTURE OF CELLULOSE AND THE LIKE Antonin Lemberger, Prague, and Lubomr Lemberger, Pilsen, Czechoslovakia Application February 17, 1931, Serial No. 516,526 In Czechoslovakia, February 17, 1930 31 Claims.

This invention relates t@ process for digesting cellulose and similar materials which avoids various disadvantages of known processes such as those in which the digestion is carried out in stages and obtains various important advantages. The new process consists in this that during digestion the material to be treated is passed contin- .i uously through a series of as great a number of digesters as possible which ensures a uniform uninterrupted operation. In this way it is also possible to secure -an uninterrupted feeding of the necessary chemicals into and through the apparatus and their conveyance away.

The'process according to the present invention and its advantages will be best understood from the description of constructional examples, suitable for carrying out the new process. IIn the accompanying drawing Figure 1 shows Lfthe rst constructional example diagrammatically in vertical section.

Figure 2 ,shows a modied construction of the pre-digester.

The digester shown in Fig. 1 consists suitably of a first digester of as large dimensions as possible, the so-called preliminary digester 1, and of a main digester 2 which is disposed next to it, preferably somewhat lower, and may be smaller. Next to this main digester 2 preferably at the same height and of the same size is a third digester, the 'so-called enriching digester' 3 as a quiescent digester and next to the latter, preferably at the same height, a fourth digester, a socalledfnal digester 4. These digesters may each or all of them consist of two or more superposed digesters forming groups bearing the same name and serving the same purpose.

The pre-digester 1 and the main digester 2V are connected with the bottom by a pipe consisting of a bend 21 connected to the bottom endof the pre-digester 1 and of a bend 27 connected to the bottom end of the main digester 2 and `of intermediate pieces 24 and 25 of the so-called separators. The separators have an outer casing consisting of an acid-proof material, preferably acidproof cast steel, or are provided withan acidproof inert lining and an internal, preferably cylindrical sieve of resistant material. 'I'he ypulp cannot penetrate into lthe space between the casing and the sieve of the separator, but the liquid, the gasesl and the steam can do so. The outer casings of the insertions 24 and A.25 are provided with branches for connecting up pipe lines `82. To the separator 25 is connected a nozzle which extends into a stuffing box 26 connected to the bend 27.. Inthis way heatv expansions in the plant (Cl. SRF-7) are compensated. Between the bend 27 and the digester 2 is a further insertion (separator) 31 similar to the insertions 24 and 25, which is provided with a branch for connecting upa pipe line. The bend 21 is provided at the bottom with a bell-shaped extension 23 in which a sieve 22 is inserted. To this extension 23 there is connected .on the one hand a pipe line 71 and on the other hand a riser 61 for wet steam and liquor and at the side branch a branch-pipe 77 for superheater steam. Similarly the bend 27 is also provided with a bell-shaped extension 28 containing an inserted sieve 29 andconnected with a riser 72 and 62 and abranch pipe 78 both for wet steam and liquor. The main' digester 2 and the quiescent digester 3 are connected at the top by a pipe.V This pipe consists of a bend 33 which is connected with an interposed separator 32 to the main digester 2. From the separator 32 a pipe line 32 is branchedoff. This bend 33 is also provided with a branch having a bell-shaped closure 35 and an inserted sieve 34, to which the the iinal digester 4 by a bottom connecting pipe which again consists of a bend 21 with a branch and a bell-shaped closure 23 having an inserted sieve 22, to which is connected a pipe line 73 and in the digester 3 a riser 63. To the bend 21 are connected the insertions (separators) 24 and 25 from which pipes 91 branch off. To the insertion 25 there is again connected the connecting pipe with a stuling box 26, which leads to the bend 27 which is connected with an interposed separator 31 to the digester 4. To the separator 31`are connected pipe lines 96. On the bend 27 is a bell-shaped closure 28 with an inserted sieve 29, pipe lines 74 and 79 and a riser 64 being con o nected thereto.

The first and the last digester Aare provided at the top with an extension of the digester neck, le and 4g which is made of as large a diameterV as possible; The extension 1e of the rst di- 'gester 1 widens conically downwards and mainly serves the purpose of mounting the automatic regulating and feeding device for the raw material with a casing forivforming a compacted plug of material in the superposed part 14 forseparating the gas and the air, for mounting the au- 4conically downwards or upwards.

these two separators 15'and 17 maybe utilized for providing a steam space by the provision. of an extension 16 of any suitable length.

The extension 4g of the neck of the last digester 4 mainly serves the purpose of mounting` a regulating device for an automatic pulp over.- flow 46 and for containing the liquor separators 41, 42 and thegas and steam separator 47. This digester extension 4g is either cylindrical or flares The two digester neck extensions are connected by the digesters 1, 2, 3, 4 so as to be in communication with one another and assist one another in regulating the liquid column in the digester system. Above the separator 15 and the intermediate piece 14'is a separator (air separator) 11, to which is connecteda pipe line 113 for conveying away air. Above this air separator 11 is an end piece (cowl) `10, to which is connected tangentially` ampipe 112 for introducing the material mixed with air. This end piece 10 is only lightly covered.

In the insertion (separator) 11 and partly in the extensions 14 and 10 there moves a stamper 13 in the form of a cone, a hemisphere or the like which is connected to a guide bar 115 which haslateral teeth on its upper part which projects to the outside. With these teeth a partially toothed wheel (toothed segment) 118 meshes. The latter is driven through transmission gear 117 by a motor 116. When the toothed segment 118 engages with the rack 115, the stamper 13 is raised. As soon as the last tooth of the toothed segment 118 ceases to engage, the stamper 13 falls on to the introduced material, whereupon on re-engaging with the toothed segment 118 it is raised again. In this way they raw material is compacted in the insertion 14 and thus forms a plug of material (separating wall) which separates the gases in the digester from the outside air. The rack 115 bears a stop 115 which moves between two stops on a contact disc 119 of a rheostat and thereby influences an electric motor for feeding the raw material through the pipe 112, thus automatically regulating the feed.

'I'he insertion (separator) 18 is connected to a vessel 12.0 containing liquor, in which a loat 121 moves, which by means of its guiding rod influences either a rheostat for regulating a pump motor for the feed of the additional liquor or, through a system of levers 122, a regulating member 123 for the feed pipe 124 directly, the arrangement being such that the additional liquor is fed into the insertion (separator) 18' in such a manner that the level in the same remains constant. A regulation of the circulating liquors and of the digesting liquor may be effected in the same way.

For the raw material a storage hopper 110 is provided at the lower tapered end of which a blower 111 is mounted, so that the raw material is drawn by suction from the storage hopper and is blown through the pipe 112 in to the top part (cowl) 10 tangentially and draws the air bysuction through the sieve 12 of the insertion 1l and the pipe line 113, 114 which is flared at the bottom into the lower end of the hopper.

- ceases to rotate.

In the extension 411 of the nal digester 4, in the upper part of the same, two insertions (liquor separators) 41 and 42 and lateral connecting branches for a common pipe 96 (for conveying away the liquor) are provided. To the upper insertion 42 is connected an extension 43 of the extension, to which is connected laterally a chamber in which an overflow 46 is provided. The height of the upper edge of the overflow weir can be balanced by vertically sliding its upper movable part, for instance by a counterpoise, or can be regulated by means of a float 44 provided in the extension 43 and connected with the Weir by a cord 45. To this overflow is connected a pipe `for conveying away the completely digested pulp, for instance to filter coils 139 or the like.

In the constructional form shown in Fig. 2 the stamper 13 according to Fig. 1 is replaced by a vertical worm 13 which is driven by means of a worm-wheel transmission gear 117 from a counter-shaft 116 or by a motor and owing to its rotary motion smoothes the surface of the introduced material.' The shaft 115 of the worm 13 is capable of sliding up and down in the hub of the horizontal worm-wheel, but is coupled with` the same by means of a spring and groove so as to rotate with it, such that when the supply of material becomes too great the worm 13 works itself up in the material, carrying its shaft 115 with it, which with its milled-in teeth displaces, a rotary rheostat 119 and thus regulates the motor for the supply of the raw material. The backlash is then formed in the rheostat 119 itself. The material may be fed either by means of the blower 111 according to Fig. l or by means of a conveyor worm 118', as shown in Fig. 2, or by employing any similar known arrangements, the speed and delivery being regulated by motors and resistances, such as 119. When too much material rises in theupper stamping space of the extension 1a of the digester neck for any reason, for instance owing to a too great supply or. swelling of the material, the worm 13 with its shaft 115 rises to such an extent that the spring keys leave their grooves in the hub of the worm-wheel for preventing the parts being damaged, a further supply of raw material being stopped by the rheostat 119. The propeller at the same time As soon, however, as the level of the material has fallen again to a suiiicient extent, the further rotation of the worm-wheel will cause the shaft 115 with its spring keys to engage owing to gravity with the propeller in the guiding grooves in the hub of the wheel and to start rotating again. On the level of the material falling, the shaft 115 will adjust the rheostat in such a manner as to cause a more rapid feed of raw material.

In place of single digesters, groups of digesters consisting of two or more superposed and interconnected digesters may be used, such that they replace the single digesters already referred to. The digesters 2, 3, 4 and so on may also be so arranged that they are placed at different heights, such that by this means different pressures and temperatures and different duration of their action and the like, may be obtained. When several digesters are placed one above the other, the upper digesters may also with advantage be used as quiescent digesters, that is to say, digesters without independent steam heating.

The arrangement of several digesters one above the other may also be such that the extension of th'e digester neck lz on the first digester'l may be completely omitted (Fig. 2). The main adl 1,954,012 vantage of this is that everywhere, where thereis a frequent o r considerable wit rawal of incompletely digested pulp in front o the weir 46 at the end of the final digester 4, either for the purpose of lling a so-called improving digester or for other purposes,l owing to such an upper digester being of greater circumference, the liquid column cannot sink so low that this would, by altering the pressure, have a detrimental effect on the digestion as might occur through improper handling in simple tubular extensions 1a with their relatively small circumference.

A further advantage of such upper digesters is, that with their large capacity, they serve more advantageously as impregnation digesters in which the pulp remains longer and thereby undergoes an advantageous impregnation for a longer time.

The principal object of such upper digesters is that with their large capacity they prevent a mixing before the proper time of the raw and scarcely impregnated material with the partly digested mass which might occur through oversights in the operation of the steam inlet, so that the pulp instead of being heated and fed forward quietly, is stirred up and mixed. In this way, a non-uniform digestion of the material would be caused which, in the subsequent digestion, would have to be repaired as far as possible at the cost of the amount and the quality. It is, therefore, better the more transferences there are, that is, the more digesters are arranged above the preliminary digester and the higher the position of the uppermost digester. The digesters may become gradually smaller towards the top.

Fig. 1 illustrates diagrammatically 'an arrangement according to the invention with two pre-l liminary digester, arranged one above the other, and two final digesters. Fig. 2 is a modification of this arrangement with-three preliminary digesters.

A digester'lb, if necessary 1b, 1c (Fig. 2) above the pre-digester 1 is arranged at a suitable height such that the uppermost digester 1b or 1c reaches up to the regulating device 120 to 123, which serves the purpose of maintaining the height of the liquid` column in the digesters. They predigester 1b issmaller than the lower pre-digester 1 andthe pre-digester 1c is also smaller than the pre-digester 1b. (The separator 18 is connected directly to the uppermost pre-digester 1b or 1c).

Where a large, old pre-digester 1 (Fig. 1) is available, and there is not room for two upper ldigesters 1b, 1c (Figure 2), or where an old construction does not allow of such a load, the lower larger digester may be divided into two digesters 1 and 1a which may be effected for example with sulphite digesters lined with concreteby means 'of a concrete intermediate cover 148. This in,- termediate cover has in the middle a large passage opening to which are joined, above and below, walls connecting it with the wall Vof the digester so that they do not obstruct the passage of the raw material from above, and all the gases and vapours from the below. In digesters which are not lined with concrete, for example for the alkali process, such an intermediate. cover may be constructed of sheet metal, there being` an annular hollow space in the intermediate cover. The 'intermediate cover 148 is preferably so constructed that the lower part 1 of the digester remains larger than vthe upper part la..v 1 All these' adaptations have the further advan- 7" tage that in exceptional cases, more particularly have no bad effect.

when forced production at the expensel of quality is necessary, in the lower digester, or in the lower part 1 of the digester, the material can be pre` digested above the boiling temperature instead of being merely heated without considering the agitation or mixing of the material which is so much less dangerous and more similar passages 148 there are, or the more digesters are placed one above the other and the higher the uppermost pre-digester is arranged. In this case also, inattention to the operation of the steam inlet can The division of the large pre-digester 1 is also to be particularly recommended where only a single pre-digester with a high extension le of the neck of the digester is used (Figure 1).

The connections of the pipe lines and other auxiliary arrangements in the example shown will be best understood by the following description of the mode of operation.

The height of the upper digester neck extension leon the digester 1 is made to correspond to the working method adopted in each case. For the sulphite process, for instance, three atmospheres will suflice in the middle of the digester and a corresponding liquid temperature of about 134 C. which corresponds approximately to a liquid column of about 20 m. This will already allow of the production of a nice, white, rm cellulose. In order to obtain a greater production, a longer extension of the digester neck (superposed part) is preferably used. In the conditions shown in the drawing, in Fig. 1 for instance, the pre-digester is assumed to be 16 m. high and the superposed part up to the level of the liquor, that 110 is, up to the rst separator 18 about 18 m. high. This corresponds in the middle of the digester to a liquid column of 26 m. and in view of the great density of the digester contents to a pressure of about 3%-3% atmospheres and a liquid 115 temperature of approximately 14o-141 C. In the middle of the lower calotte this will already correspond to a pressure of 41A atmospheres and a liquid temperature of about 14S-146 C., although far lowerv values would. suffice for the preliminary digesting process.

The other digesters 2 and' 3 measured in the middle of the digester have in view of the great density and immobility of the mass and its conductive resistance a pressure of approximately ,A1-41A atmospheres which corresponds to a liquid temperature of about 14A-146 C. measured in the middle of the digester. Measured in the middle of the lower calotte this already corresponds to a pressure of about 31/2-4% atmospheres and 130 a liquid temperature of about 14S-150 C. In the lower connecting pipes these values are still higher.'

For obtaining greater uniformity it is advisable to use a greater number of smaller digesters, preferably several digesters superposed one on ,l the other or placed next to one another.

In the. case of the last digester, instead of or preferably in addition to the superposed part 4g, one or more outlet members (for instance slide valves) may be provided, which may be used for the frequent removal of the completely or almost completely digested pulp.

material an approximately constant material level is maintained in the superposed part 12.

`The supply of material is regulated as described above according to the demand or according to the progress of the treatment of the material. The restarting of the forward feed of the material may be notified to the attendants for instance through an electric conductor in the form of an optical or acoustic signal in a control cabin and registered there.

The constructional form for the production of sulphite cellulose shown by way of example operates in the following manner:

The digester is lled up to a certain height with fresh liquor, and, at the same time, the chaff is fed in through the superposed part 1e into the pre-digester 1 from above, steam being allowed to enter gradually at'the bottom, rst into thepre-digester 1 through the pipe'll and the perforated distributing pipe 61. Owing to the inclined position of the bottom pipe connecting the digesters and owingto the rising pressure in the pre-digester, even the still rough wood chips in the liquor will pass to the lowest part of this inclined connecting pipe where they are whirled up by the steam entering gradually from the pipe 72 through the branch pipe 78 and the inserted sieve 29 and carried away into the main digester 2. Later the perforated distributing pipe 62 -at this point also will become operative. Fresh liquor may be admitted by way ofthe regulating arrangement 12, 123 through the supply pipe 124 into the pre-digester 1, so that the contents of the main digester 2 will soon pass through the upper connecting pipe into the quiescent digester 3 and will pass from the latter through the lower connecting pipe into the iinal digester 4. In the meantime steam has been caused to enter here as well, through the pipe 74, the branch pipe 79, the inserted sieve 29 and subsequently through ythe perforated distributing pipe 64 as well and digestion has taken place actively in the main digester 2, while material has been continuously fed into the pre-digester 1. As soon as the digesters 3 and 4 have become more lled, digestion will take place actively in the final digester 4. In the upper bend 33 above the main digester 2 an injector 58 is interposed in the pipe 88. As soon as the digesting process commences in all the digesters, the injector 58 is put in operation first with live steam and subsequently with a steam and gas mixture from the digester 2, the excess liquor being thereby driven out of the main digester 2 through the pipe 32', 88 and the separator 17 into the digester li. To the injector 58 a pipe may be connected from the lower separators 24, 25 of the quiescent digester 3, for returning the circulating liquor which has been further used up in the digesters 2 and 3 back to the pre-digester 1. In the constructional form shown in Fig. 1 the liquor used up in the digesters 2 and 3 is returned through pipes 91 on the one hand to the injector 51 in the steam supply pipe '71 and on the other hand mainly by way of the injector 57 and the pipe 91, 97 to the upper part of the pre-digester 1. When the quantity of liquor becomes sufcient, that is, when the liquid column in the plant reaches the requisite height, the float 121 becomes operative and cuts off the' supply of additional liquor through 124 and 123.

As soon as the level of ythe liquid column in the final digester 4 or in its'extension or super- ,posed part 4y has reached the separator 41, the

pipe 96 is connected to the lower injector 52 in the steam pipe 72 for the main digester 2 and the rst fairly rich circulating liquor is pumped over from the nal digester 4 through the perforated distribution pipe 62 into the main digester 2, even highly superheated steam being suiciently cooled down or moistened by the liquor without loss.

During the further course of the Adigesting process a branch pipe 78, can deliver from the lower injector 52 into the lower connecting pipe 27 between the pre-digester 1 and the main digester 2, so that the first fairly pure circulating liquor from the nal digester 4 or some other pure and good liquor is forced in at this point as a washing liquor, after the nal liquor from the predigester l in the separators has been allowed to flow out through the pipes 81, 82 into the receiver 48. This washing liquor removes most of the iinal liquor still adhering to the material, is separated off again in the separator 31 and conveyed through the pipe 91 to the injector 57 which forces the washing liquor into the pre-digester 1, where it is utilized again and led off with the completely spent final liquor. The completely spent, highly heated final liquor which has been freed from gas by the superhea'ted steam and has been conveyed into the receiver 48 is completely freed in the said receiver owing to sudden expansion from SO2, which gas is led away for being recovered and the resultanthot waste liquor, freed from SO2 and greatly enriched with incrustations, can thereupon be easily treated without the addition of live steam, so as to obtain various by-products.

Besides the receiver 48 another receiver 49 placed at a higher level, namely in the neighbourhood of the upper end of the superposed part lz may with advantage be provided, which is connected to the lower receiver 48 by a pipe 83 which has a number of `apertures 83' opening at different levels in the receiver and provided with closing means. The upper receiver 49 has an outlet 85. The upper receiver is lled only up to the level of the overflow 85, while the lower receiver 48 is full.

When the apparatus is operating normally the fresh liquor is also fed to the final digester 4, being introduced through a pipe 147 into the separator 3l between the digesters 4 and 4b above the sieve in the separator so that the pulp passing into the last digester is treated with fresh liquor. 125 'I'he digesting liquor separated off in the separators 41 and 42 for the injector 52 is therefore used up to a relatively small extent, so that with or without an addition of SO2 it is very effective in the main digester 2 and in the enriching digester 130 3 acting as a quiescent digester and is then added for being completely used up through the pipe 91, 97 and the injector 57 in the digester 1 to the fresh raw material.

As soon as it has been found by taking samples 135 that the cellulose in the upper part of the superposed part 42 of the nal digester 4 or in the overflow chamber connected to the latter has been sufliciently digested, the over-ow Weir is properly adjusted, so that the pulp will flow fairly uni- 140 formly to the rest of the plant in which it is being treated.

The gases mixed with steam coming from the receiver 49 are led away through the pipe 86 by, way of the separators 17 and 15 and the pipe 90. 145 The common pipe 90A meets the pipe which branches off from the upper part of the superposed part 4g through the separator 47 and through which the gas and steam mixture from. the nal digester 4 is conveyed away. The two pipes are 150 connected up to an injector 60. The vapours are in this injector condensed by the waterunder pressure coming through a pipe 104 and the gas and water mixture is conveyed through a cooling plant 107--108 in a tank 50 for causing thegas to be absorbed and for obtaining the so-called gas liquor (that is, free, aqueous sulphurous vacid or water and condensate enriched with gaseous SO2) The gas liquor thus obtained is conveyed through its own higher liquid column through a pipe 108 back to any of the digesters, preferably to the quiescent digester 3 through a branch 40, where owing to the material being in a quiescentstate there is no such great danger of the rapid disintegration of the liquor as in the other digesters. Instead of usingfresh water from the mains the injector 60 can also be fed with a fairly rich liquor pressed out of the finished pulp through the pipe 130, which liquor is separated oi in the iilter presses 139 and is led through the pipe 109 into an absorber 100, is atomized in the latter and preliminarily enriched with freshly produced or compressed SO2 gas from the pipe 144 and conveyed by means of a circulating pipe 101. The excess delivered by the pump is caused to pass through a branch pipe 102 into the same absorber 100 where it is atomized, to circulate continuously and to be enriched with SO2. A further pipe 98 connects the absorber 100 with the injector 58 for further conveyance to the separator 17 or to the digester extension 12: of the pre-digester 1. 'I'he injector 58 which was at lrst driven with fresh steam is when in full operation fed with the steam and gas mixture from the main digester 2, which has been separated by the sieve 34 in the extension 35 from the pulp and has accumuated at this highest point, the circulating liquor from the sepa* rator 32' and the cooled, enriched, pressed-out liquor from the absorber 100 being further heated and if necessary enriched.

For producing the lgas liquor a new process and a new apparatus are used, consisting in this, that the liquid intended for the absorption of the gases passes preferably under pressure i5 through the suction and pressure injector 60, be-

ing at the same time u'sed as the driving medium for the latter or by way or a nozzle or mixing arrangement mixed with the SO2 gases first into a drum 107 which is disposed in cold water in an outer vessel 50. In the-drum 107 the mixture of liquid and gas is guided to the bottom ofthe vessel through a pipe which is perforated in its lower part. The gas not yet absorbed in the pipe rises again in the drum 107 in the J5 form of bubbles and is thus further absorbed in a finely divided state. The remainder of the gases collects under the upper end wall of thedrum 107 and is drawn in by suctionagain and again through the pipe which where it enters the drum 107 is formed as an injector, or throughan injector part extending into the drum or similar arrangement by the pressure liquid and driven ,o to the bottom of the drum 107. By this means the liquid is thoroughly saturated with SO2 gases. In this case of over-saturation the remainder of the non-absorbed gases passes, finely divided in the liquid, with the latter through a cooling coil 108 connected to the drum^107 and lying in water, in which coil further absorption takes place owing toV a further cooling. The gas liquor thus produced is then itself passed under the action of gravity-into the quiescent digester or digesters 3 which are under full pressure, but more par- 75 ticularly lfor the impregnation of the' raw mateare suitable which have proved satisfactory in ous digestion'. A

rial into the separator 17. For this reason this arrangement is placed at a suitable height.

The over-ving cooling water which has been heated vin the coil vessel 50 is conveyed through a pipe 106 into the upper part 43 of the superposer part 411 of the nal digester 4, where it dilutes the pulp before reaching the Weir 46 without chilling it, so that the digested pulp can be easily washed and bleached.

The superposed parts lz and 4e of the digesters and bends 21, 27, 33, 38, the insertions 26, 37 and the casings of the separators 24, 25, 31, 32, 41, 42, 47, 11, 15, 17, 18, will preferably be made of a special metal or special steel, which is capable of resisting the action of liquors or acids.

For subsequent treatment or improvement with alkaline liquors it is preferable to erect separate improving digesters for which purpose the rotary agitating digesters of iron or steel the sodium cellulose industry. It will be found advisable to make such improving digesters of so-called non-rusting acid-resisting steel or iron with rivets of the same material, in which case the riveting may be carried out in the cold state.

The improving digesters are with advantage connected to the final digester 4, the arrangement being such that the iirst improving digester 130 is directly connected, as indicated in the drawing, and. then the other improving digesters are connected by means of extended branches of a double cross pipe 125 in both directions (not shown in the drawing).

Inthe drawing there is shown by way of' example a direct connection with theiinaldigester 4, which connection might be made on three sides of the riinal digester by means of a slide valve 67, a slide valve 68 and by means of a slide valve 126 which is connected by a pipe to the slide valve 30 below the final digester 4. All these slide valves lead to the cross-piece 125 which is connected over a further slide valve 127 with the hollow gudgeon 129 of the agitating digester 130. Behind the slide valve 127 are connected a steam pipe 69 and a supply pipe"`128 for `liquor or washing Water. One arm of the double crosspiece 125 may be provided with a small pulp slide valve for the withdrawal of samples, the other lateral arms being closed by blind anges so as to allow of further improving digesters be,- ing connected up. The double cross pipe 125 can, however, as, shown in the drawing be connected through the slide valve 30 to the lower connecting pipe 27 leading to the digester 4 so that should occasion arise it is possible to withdraw a less-digested cellulose.

The liquor outlet pipes 93, 95 and 133 from the improving digester may be connected to the digesting liquor pipes 94, 54 and 96 for continu- According to the invention, the internal pressure in the various digesters is produced not by steam butby a liquid column whereby a liquid temperature corresponding to this liquid column can be obtained. 'l'.'he values are dependent not 140 only on the height but also on the density and the different rcsistances of` the pulp in the di-4 gesters, which factors may be made as high as is required by the raw material and the kind of digesting process employed.

For producing sodium and sulphate straw cellulose, the normal plant shown in the drawing will suiilce, even for very large. outputs. As, however, when producing cellulose from our cereal straw, maize, rice, esparto, bamboo, reed and 150 the like raw materials containing `much salicic acid, the recovery of the soda from the liquors is made diilicult and uneconomic by the accumulation of salicic acid, it is preferable with the new process to pre-digest with sulphite liquor and only at the end to re-digest with sodium liquor. In this case only small quantities of alkalies will be required, the final liquor of which may be atomized with great advantage to the sulphite digesting liquor for the preliminary s'ulphite digesters, where it can still do good service and when completely spent be used with the sulphite waste liquor` for various by-products. With this combined and cheap process instead of a brown pulp a whitish pulp is obtained which can be easily completely bleached, is much rmer and has many more valuable properties than the brown pulp hitherto obtained by the costly sodium or sulphate process. y I

For producing the sodium and sulphate wood cellulose for which the resinous pinewood, the red beech and similar kinds of lwood are suitable, the plant shown in the drawing can be used for the purely alkaline process but without an inner lining, being, however, constructed for a greater pressure. It is simpler, more rational and preferable in this case as well, when employing the new continuous digesting process, to work according to the cheaper sulphite process'as described for straw pulp and only at the end to redigest with the expensive alkaline liquor.

By the arrangement of several digesters one above the other, it also becomes possible to vary the treatment oi' the last digesting liquor which is thoroughly saturated with incrustations and is, therefore, too thick for impregnation, and this liquor is added only to the raw material which has already been fully impregnated in an upper digester. It is taken by the separators 24, 25 from the passage between the digesters 3, 4 and by means of the conduit 91, the injector 57 and the conduit 97, is fed into the pre-digester 1 (Fig. l) at the top, or into a separator 19 between the pre-digesters 1 and 1b or 1c and 1b (Fig. 2). For impregnating the raw material which is fed from the storage container 110 by means of fans 111 througha feeding device, for example 112, 113, and is-preliminarily steamed in the preliminary steamer 16, it is of advantage to use a thin gas liquor, or single gasliquor, which is obtained from the residual gases in the recovering apparatus 50, and is introduced through the pipe conduit 87. This thinly liquid and concentrated gas liquor forces its way into the pores of the bres which have been opened by the steaming and swelling and in between the fibres of the raw material whereit combines with the gases which have already forced their way in and which have risen from the lower pre-digester or are fed to the separator 17 from the main digester 2, from the conduit 86 and from the upper receiver 49 through the conduit 86 etc.,

and thereby causes that in the subsequent digest# `ing of 'the material the decomposition begins in the interior and proceeds from the inside towards the outside so that through the introducl tion of the thick last circulationliquor, which contains much incrustation. the premature decomposition of the exterior fibre layers is avoided since these outer bre layers remain protected from premature decomposition and attack by the incrustations which surround them.

In order that the entry of this end liquor which has been completely used in the large pre-digester 1, into the main digester 2, and the 1.111-

. necessary dilution of the better digestion liquor supplied there may be. avoided, there is placed between the pre-digester 1 and the main digester 2 a pulp washer which consists in this, that in the separators 24 and 25 interposed in the lower connecting conduit between the digesters 1 and 2 the end spent liquor is removed as long as it ,shows that it is completely used up, if necessary, until the material is completely thickened.

The exhausted end liquorv may, for example, in passing out of the pre-digester 1, be further treated in the knee piece 2 with superheated steamwhich is supplied through the branch 77 of the conduit 69, 71 below the sieve plate 22. At this stage, superheated steam does no harm but decomposes the end liquor to such an extent that it drives out the SO2 gas and carries it back into the pre-digester 1.

The pulp which is to pass.from the digester 1 into the digester 2 is concentrated, that is, it is to a large extent freed from the spent wasteliquor accompanying it, but the gas' liquor forced into the'pores and the iirmly adhering incrustations go with it. The pulp thus reaches the lowest part of the connection in the inlet knee 27 under the main digester 2 where it is diluted and agitated by the steam liquor mixture which enters through the injector 52 and the branch tube 78 under the sieve plate 29. The better digesting liquor used here ows through the conduit 96 to the injector 52. The waste liquor still adhering to the exterior of the pulp is thereby washed away, while the impregnating liquor which has been forced into the raw material and the firmly adhering incrustations suffer little loss, because the operattion proceeds rapidly and in the following separator 31, shortly before entering the main digester 2, the resulting washing liquor is again withdrawn and led to the injector 57 through a tube 91, which injector delivei s it together with the circulation liquor supplied through the conduit 91, from the digester 3 through the pressure conduit 97 into the separator 19 or through a perforated distributing tube or the like, directly into theIpre-digester l.

\ The pulp which again has been concentrated by the removal of thelliquor in the separator 31 and has been completely freed from the waste liquor, that is, has been thoroughly washed, isdiluted at the same time in the digester 2 with the above mentioned better circulation liquor through the perforated distribution tube 62. From the last digester 4 in which the fresh liquor introduced is only slightly exhausted, and inthe upper separators 41, 42 of which the liquor is separated from 130 the digested cellulose and led through the pipe conduit 96 to the injector 52 and in this with the steam, if necessary, superheated and mostly absorbed by the liquor, it is heated so that only any excess remaining after suiiicient cooling or mois- 135 tening is delivered together with tho heated liquor into the main digester 2. y

A similar washing may take place during the digestion with small 'deviations and under the digester 4. A closer description of Athis is not 140 necessary, since the process will be quite clear from the drawing together with the above description. For washing the pulp before entering the last digester proper, the pure fresh liquor is always used as washing liquor. The resulting liquor 145 (mixed liquor) which is withdrawn after the washing is always led back one stage, that is into the preceding digester, so that the liquor is entirely used up.

In the second or a further removal of the di'- 150 gestion liquor, its decomposition -is not carried out by directly supplying superheated steam, because at this stage superheated steam introduced directly would damage the pulp.

In the main digestion in the digester 2, the internall'y impregnating gas liquor, is also digested, so that a part of the interior incrustation is released and passes over into the digestion liquor. This digestion liquor (circulation liquor) is, for the most part, withdrawn from the pulp again in the separator 32 on leaving the digester 2 and is supplied through a tube to the injector 58 in which it is mixed with the concentrated pressed liquor comingI from the concentrating apparatus 100 through the conduit 98, and, further, is enriched with the gases from the digester 2 collected in the superposed part 35, 36, and is driven in a hot condition through the pressure conduit 88 into the separator 17 before entering the pre-digester 1c or the superposed part 12 (Fig. 1). There the liquor is mixed with the strong gas liquor flowing in through the conduit 87 and is drawn away forl impregnating the raw material, while the small amounts of incrustation carried with it begin to adhere to the outer layers, which process is assisted by diffusion. Where an intermediate diffusion digester 1b .(Fig. 2) is present, this enriched liquor with'little incrustation may also be introduced before the raw material.

f Also,` the main digester Zand the enriching .digesterffquiescent digester) 3 may consist of two*ormoredigestersplaced one above the other. `From'ftheWmain digester 2 the pulp passes through the upper connecting pipe 32-38 -into the adjacent digester.` In this quiescent digester the impregnation liquor which has been digested in the main digester 2 and which has been partly removed is replaced by concentrated thin liquid gas liquor with the object of further impregnation or is enriched; the further impregnating process is assisted by diffusion in the quiescent state. The strong gas liquor is led from the recovery apparatus through the conduit 108 into the sieve chamber 40 and through its sieve plate 39 into the upper knee piece 38 of the digester under the action ofgravity. The mixed liquor in the quiescent digester 3 can also be concentrated by the digester waste gas or compressed SO2 gas introduced'in the opposite direction through the perforated distributing tube 63 and supplied through the conduit 145. V

This renewed impregnation is the principal object of the quiescent digester or the quiescent interval and has great importance for the further digestion process. In the further digestion process the procedure is repeated as'explained above according to the number of digesters. The more often the pulp is further impregnated during a quiescent interval in the digestion, the more uniform and capable of being bleached is the pulp. For this purpose and, for example, a construction with an upper quiescent digester and a further quiescent digester may be employed.

The individual digesters are connected in series by stuflngbox tubes20, 26,37, which act. at the same time, as extension members which make possible easier replacement of the packings and also Vmakethe vibrations or stressesof the digesters harmless.

For preliminarily steaming the raw material i whichis introduced, it isalso possibleA to use exhaust steam is used in the upper part of the predigester, a great saving in live steam is obtained.v

liquor from the various excess gases or waste gases, but indirectly through the pre-steaming apparatus 14-17 where this and similar gases and vapours are usefully employed, and are partly absorbed. Only the residue cooled by the fresh raw material is sucked into the cooler 107 of the so-called recovery apparatus 50 f )r absorption in the pressure liquid for producing the gas liquor through the separator l5, the pipe conduit 90 by means of the liquid injector 60, which is driven by the pressure water 104 orby the pressed out liquor 103 which has been enriched in the enriching apparatus 160 and put under pressure by means of the liquor pump 101. The same applies to the gas steam mixture in the pipe conduit which operates the injector 58 and originates in the main digester 2.

Below each upper digester (1b, l1c and 4b) there is interposed a separator 19 which serves to introduce SO2 vin gaseous form, if'necessary, in excess through conduits 99 or 141. or 146. In thislway, on the one hand, the spent digesting liquor (circulation liquor) may be concentrated and the impregnating and acid bleaching process furthered, and on the other hand, more gas liquor, partly serving this purpose, but acting more quickly can beproduced. The same applies to the introduction of the compressed gases in the ,quiescent digester 3 through the inlet tube 145 and the perforating distributing tubes 63, and to the gas inlet 144 in the enriching apparatus 100.

The separators :1 9 also serve for` introducing circulation liquor (digestion liquor) for example into the pre-digester or to gas liquor into the upper final digester (bleaching or acid bleaching digester) 4b (Fig; 2) through a conduit 147.

, The main digester 2 has at the top at the highest point of the connecting pipe on the knee piece 32 a gas vessel 35, with a lower sieve plate 34, for keeping back the pulp and with a connecting pipe to the injector 58 which is joined to the cover 36,

set free in the two digesters. In the gas vessel 35, the escaping gases and vapour collect more easily above the sieve plate 34 and the more uniform removal of gas and operation of the upper injector 58 is ensured. The removal of the pulp may also occur prematurely, that is before the over-flow 46 either periodically, for example for filling the improving digesters, or partially and continuously for simultaneous working upof a par@ of the cellulose which is not completely digested. The removal is then effected, for example by means of a pulp slide 67 and 68, onl the nal digester, or by means of the slide valves 30 on the lower connecting pipes which also are used for completely emptying the digesters for repair, in which case the residual pulp can be completely digested in the improving digester.

As a rule, however, the pulp is recoveredA in the extension of the neck of the digester of the iinal digester 4 or4b, or in the superposed part 43 connected with the nal digester beside which the adjustable overflow slide 46 is built. The adjustment slide of the overflow slide valve 46 is, of course, always so much smaller than the slide .of the front liquid column the greater are the losses in the operation which are caused by the immobility of the compact mass and resistances for operating the injector with the gas and vapour pressing devices, and the like.

in the curves, passages and narrow places, com- 'Ihin pulp requires a higher thicker pulp, a loweradjustment of the over-flow slide 46. This adjustment is, however, effected automatically by connecting the overilow slide 46 through a rope 45 with the float 44 in the superposed part 43. When there is a larger pressure onthe float 44 through the iloating in of the thinner pulp, the float 44 rises and allows the over-ow pulp 46 to sink so that more thin pulp can ow away. If, on the other hand, the pulp is thicker, its flow into the superposed part 43 is less rapid, the float 44 sinks and raises the over-flow slide 46 s'o that less of the thick pulp ows over. Consequently, on the one hand, the liquid column (pulp column) above the pre-digester cannot rise or fall too far, and consequently the ow of pulp for treatment is uniform and independent of the thickness of the material, of thick pulp less and of thin pulp, on the other hand, more is allowed to pass on the slide 46; both pulps, however, are compacted in the worm members 139 to the same density, and consequently also to the same amounts after which only they are delivered to the mills and then again diluted to the same amounts and further treated. The liquor pressed out which is still good but diluted by the warmed cooling water supplied through the conduit 106 is introduced into the enriching apparatus 100, as far as -possible in an atomized state through the conduit 109, in which apparatus it is enriched with the pure SO2 gas (for example compressed SO2 gas) introduced through the pipe 144, or the'like. From this enriching apparatus 100, which may preferably consist of larch Wood, the liquor containing gas which is kept in circulation by ,the pump 101 is, therefore, well enriched, and is partly passed through the conduit 98 to the injecton, and is, further, used for impregnating the raw pulp, while a part is circulated through the conduit 102 through an excess pressure valve provided in the pipe vconduit 103, or is forced through the pipe 103 into the recovery apparatus 50 wherethis liquor instead of pressure water or together with the same, operates the injector 60 an/d is further considerably enriched. Several such enriching apparatus 100 and, more particularly, several recovery apparatus 50 which are connected by any pipe conduits may also be erected.

The gases and vapours which rise from the inished pulp in the superposed part 43 are likewise led through the separator 47 by a pipe A105 to the suction and pressure injector 60 where, together with the exhaust gases supplied from the preliminary steamer 16 through the separator 15 and the conduit 90 they are used in the recovery apparatus 50, (as above described) for the production of gas liquor.

The sulphite digesters have hitherto been lined with an acid-resisting lining. This has hitherto been made of sheet lead but now is only made oi acid-resisting concrete and tiling or the like which often requires repairing and other large expenditure. According to the present invention even for the sulphite process unlined digesters are used which may consist not o! ordinary steel parts of such materials screwed ,together by means of flanges or of such or similar materials or compositions or alloys cast in separate parts, which are left rough on the inside and are screwed together at the outside, the flanges forming stiiening ribs. Different materials of the ,same or similar properties may be used for different parts. Cast and screwed digesters will naturally be used more for smaller digesters, for example, for the upper digesters of the continuously working digestion plant in which the pressure is so small that digesters of special cast iron may be used directly and without danger, more particularly because in them, and also outside there are no considerable variations of temperature. For the large and lower digesters riveted digesters are preferably used. Amongst the materials referred to steel alloys, for example, chromium, nickel, molybdenum, steel, amongst others, and also iron alloys as, for example, the so-called neoferrochrome and,l nally, the so-called iron-bronze amongst others, may be used.

Instead of the injectors, partly or wholly rotating pumps may be used for the liquor circulation, in which case it is directly possible to introduce the digestion vapour into the pressure conduit so that this does not reach the digester alone and directly, and possibly in a superheated state,`but is taken up by the liquor and only any excess in a cooled or saturated state is carried with the liquor into the digester in nely divided form. In certain circumstances steam of lower pressure than the prevailing digester pressure. such as waste steam and exhaust steam. may be introduced into the suction conduit through nozzles distributed at various points and so introduced tothe digester. Theintroduction of such low pressure steam into the suction conduit, more particularly when the liquor is being supplied, may preferably be carried out near to the pump where the pressure is equalized.

The separators used in the arrangement described can also be cleaned during the operation, that is, the inner sieves may be freed from fur, pulp residue, mud and the like, by nozzles or spraying tubes, roses or the like ,for live steam, gas or solvents being arrangedv between the casing and the inner sieve. These media may be, introduced separately or together.

The cellulose produced according to the method 125 described may be bleached with alkaline manganates, peroxides, hypochlorites, aqueous solution of chlorine, chlorine gas or other media. All these and other treatments may with advantage be carried out in the so-called improving 130 digesters 130 connected to the end digester. The digested cellulose is introduced into the improving digester, is there freed from liquor, if necessaryis pressed with steam, air or gas pressure, is Washed and if necessary pressed out again, 135 then a part is mixed with a bleaching agent, is again compacted and washed and in the unbleached condition further steam is injected or the material is completely bleached. lIn this case f the bleach with aqueous chlorine solution or even 140 with pure chlorine gas bleach can with great advantage be led directly trom the tanks with liquid chlorine according to the raw material to be treated. In order to assist the bleaching process in the improving digesters at a suitable time, 145 for example, air, oxygen, carbon dioxide or a liquid dilute acid or another agent which assists the bleaching action may be added during the operation. i

The apparatus according tothe inventionis 150 'also especially suitable for carrying out a pure or' nearly pure gas liquor, that is aqueous solution of the SO2 gas or free sulphurous acid without or 'with very small additions of lime or other bases. v

lIfhis method which perhaps has hitherto been known only through laboratory experiments has very many advantages and-in all casesiwith the assistance vof this apparatus can be used in factory operation since only in this or a similar apparatus can the very unstable gas liquor which very easily loses thegas which is only loosely absorbed be advantageously employed.4 This liquor is continuously concentrated during the digestion process and the gas set free is mostly carried along with vapours or mixed therewith, while the excess of this-gas is used continuously and in the shortest way for concentrating and for producing new gas liquor.

The advantages of such a method of digestion with free sulphurous acid at a very low temperature but under-suicient pressure are very important as regards the output, strength, purity and capability of bleaching of the pulp, sothat a great economy is the result especially with the low price of liquid sulphurous acid prevailing on the apparatus and on the libres.

including tower operation and the separate reat the present day. y c Through the use of liquid sulphurous acid a series of expensive arrangements can be dispensed with, more particularly the inconvenient liquor plants from the treatment of pyrites up to and covery of the waste .gases which, however, is only partly effected in periodic operation.

The liquor referred to better called acid as distinct from the lime-containing liquor from the towers, is chemically and mechanically quite pure without loam and earthy substances, without arsenic, selenium, iron and the like,.and does not deposit any lime, either mono-sulphite or gypsum, The iibres remain pure and therefore form an excellent pulp which is especially suitable for articial silk, morel particularly transparent artificial material, the best kinds of paper andlsimilar valuable products. The apparatus may forthwith be constructed more particularly for -this purpose, if necessary, also with indirect or mixed steam heating.

' What' we claim -is:-

1. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices forcontinuously regulatingthe introy duction of the raw materials and of vthe chemicals, and devices 'for' continuously regulating the removal of the digested cellulose, the chemicals, and end liquors, the digesters forming communicating vessels in order-that the raw material may be continuously supplied and may pass through in a continuous-stream, and connectionsv between the digesters, arranged alternating at the top and the bottom, which are made to slope so l that they form an incline for the better movement of the mass.

3.' An apparatus for digesting cellulose and similar materials comprising a battery of Vdigesters, devices for continuously regulating the introduction of the raw materials and of the chemi` c a continuous stream, and sloping connecting pipes between the digesters 'and inlets for steam liquor or gas arranged at the lowest points of the connecting pipes for loosening and feeding the material forward 'at these points.

4. An apparatus for digesting cellulose and similar materials comprisinga battery of digesti ers', devices for continuously regulating the introduction of the raw materials and of the chemicals, and devices for continuously regulating the removal of the digested cellulose, the chemicals, and end liquors, the digesters forming communicating vessels in order that the raw material may be continuously supplied and may pass through in a continuous stream, and sloping connecting pipes between the digesters and an outlet for gases and vapours at the highest point of the upper connecting pipe. l

5. `An apparatus for. digesting cellulose andv similar materials comprising a battery of digesters, devices for continuously regulating the introcating vessels in order that'the raw material maybe continuously supplied and may pass through in acontinuous stream, and an automatic regulating apparatus in the inlet conduit of the rst duction of the raw materials and of the chemidigester for regulating the introduction of the.-

raw material according to the progress of the digesting process. y

` 6. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuouslyv regulating the introduction of the raw materials and of the chemicals, and devices for continuously regulating the removal of the digested cellulose, the chemicals, and end liquors, the digesters forming communicating vessels in order that the raw material may be continuously supplied and'may pass through in a continuous stream, and an automatic regulating apparatus in the inlet conduit of the ilrst digester for regulating the introduction of the raw material, and a signalling device, acted on by the automatic regulator, for indicating the state of the introduction of material. l

YL. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuously regulating the introduction of the raw materials and of the chemicals, and devices for continuously regulatingcthe removal of the digested cellulose, 'the chemicals,` and end liquors, the digesters forming communicating vessels in order that the raw n'ihterialmay be continuously supplied and may through in a continuous stream, and a pulp-overflow correspending to the height and density of the liquid column in the digesters joined to the extension of the neck of the end digester.

8. A method'of digesting cellulose and similar materials -in which the raw material passes c ontinuously through abattery of digesters on .ac-

count oi' the hydrostatic pressure inthe battery,

characterized by the feature that fresh liquor is continuously supplied to the already digested pulp, where, afterbeing slightly used up, it is continuously withdrawn from the pulp and is supplied to the preceding digester aggregate, in counter current and after repetitions, according to the number of digesters, it is iinally supplied to the fresh rawv material, and, after being used more rapidly, is led away continuously and uniformly' into the rst digester as end liquor.

9. A method of digesting cellulose and similar materials in which the raw material passes continuously through a battery 'of digesters on account of the hydrostatic pressure inthe. battery, characterized by the feature that in the continuous working process, the pulp is first treated in some digesters, according to the sulphite process, and only'then in further digesters, according to the soda process, or' any other special process, the end liquors from the final process, for example the alkali end liquors being added to the circulating sulphite digesting liquor in the preceding digesters. v

10. A method of digesting cellulose and simi- :lar materials in which the raw material passes -continuously through a battery of digesters on account of the hydrostatic pressure in the battery, characterized by the feature that` the end* liquor, after being -utilized in the iirst digester, is removed, after which the pulp before passing into the main digester is treated with. a part of a better, purer and stronger digesting liquor as washing liquor, and then is again freed from'the greater part of this liquor and is thus thoroughly washed,` after which the pulp is mixed with the next better liquor and passes into the main digester, while the waste washing liquor, in order that it may be completely utilized, is led back" into the rst digester, which washing process may also be carried out with other digesters with the passage at the bottom.

11. An apparatus, having steam injectors employedfor delivering the hot circulating diges tion liquor and means for cooling steam which entering the end digester.

12., An apparatus for digesting cellulose and similar4 materials comprising a battery of digesters, devices for continuously -regulating the introduction of the raw materials and of the chemicals and devices for continuously regulating the removal of the digested cellulosa-the chemicals, and end liquors, the digesters forming communicating vessels in order that the raw material may be continuously supplied and may pass through in a continuous stream, and means for removing the end liquor from the first digester and a branch conduit for super-heated steam arranged in front of the means for removing the end liquor through vwhich the remaining SO2 gases from the liquor are set free and returned to the digester.

13. An apparatus for digesting cellulose and similar materials vcomprising a battery of digesters, devices for continuously regulating the introduction of the'raw materials and of the chemicals, and devices for continuously regulating the removal of the digested cellulose, the chemicals, and end liquors, the digesters forming communicating vessels in order that the raw material may be continuously supplied and may pass through in a continuous stream, and passages for gases and liquor and regeneration devices provided in the passages.

14. An apparatus ,for digesting cellulose and similar materials comprising a batteryv of digestand vapour from the mass, or supplying them to the mass.

15. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuously regulating the introduction of the raw materials and of the chemicals, and devices for continuously regulating the removal of the digested cellulose, the chemicals, 'and end liquors, the digesters forming communieating vessels in order that the raw material may be continuously supplied and may pass through in a continuous stream, and-means for separating the liquids, gases and vapour from themass consisting of an. insertion, the outer coating of which is made of a material resistant to the acid, or the liquor, or is lined with such and has an inner 4cylindrical sieve consisting of a material which is resistant to the acid, or the liquor, the outer casing being provided with branches for the introduction and removal of chemicals, gases and vapour.

16. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuously regulating the introduction of the raw materials andof the chemicals, and devices for continuously regulating 'the removal of the ldigested cellulose, the chemicals, and end liquors,A the digesters forming communicating vessels in order that the raw material vmay be continuously supplied and may pass through in a continuous stream, and injectors for supplying heating steam to the digesters so that the digestion liquor is actively circulated and preheated while the steam is cooled. is'too hot and preheating fresh liquor before 17. An apparatus for digesting cellulose. and

ers, the digesters forming communicating vessels in order that the raw materials may be continuously supplied and may pass through in av continuous stream, devices for continuously regu- 1g 5 lating the introduction of the raw materials and of the chemicals, and devices for continuously regulating the removal of the digested cellulose, the chemicals, and end liquors, and extensions of the necks of the first and lastdigesters for maintaining the necessary pressure and temperature within the battery, and a separator for removing SO2 gases in the neck extension of the first digester arranged below the inlet for the raw material.

18. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuously regulating the introduction of the raw materials and of the chemicals, and devices for continuously regulating the similar materials comprising a battery of digesters, devices for continuously regulating the introswollen but still before its entry into the preduction of the raw materials and ofthe chemicals,

and devices for continuously regulatingv the removal of the digested cellulose, the chemicals,

' the upper container for the purpose of maintaining the liquid level in the digesters.

20. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuously regulating the introduction of the raw materials and of the chemicals,

and devices for continuously regulating the removal of the digested cellulose the chemicals, and end liquors, the digesters forming communicating vessels in order that the raw material may be continuously supplied and may pass through-in a continuous stream, and an upper container for the waste liquor which is placed somewhat lower than the level of the liquid columnin the. digesters, and a steamer in the raw material inlet to which the gases and vapours released in the upper container are led. Y

21. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuously regulating the introduction of the raw materials and of the chemicals, and devices for-continuously regulating the removal of the digested cellulose, the,

chemicals', and end liquors, the digesters forming gesters, devices for continuously regulating the introduction of the raw materials and of the chemicals, and 4devices for continuously regulating the lremoval of the digested cellulose, the chemicals, and end liquors, the digesters forming communicating vessels in order that the raw material ymay be continuously supplied and may Y:pass through in a continuous stream, and separators at the inlet of the rst digester for introducing and removing steam and gases, and a member disposed between such separators in whichthe falling raw material is steamed and swollen by rising SO2 gases.

23.` A method of impregnating raw material and ibres in a battery of digesters, characterized by the feature that before the raw material enters the first digester, first moist SO2 i is supplied toit and after it has swollen but still before its entry into the first digester, a thin gas liquoris supplied which in the pores of the raw material combines with the gaseous S02 which `has been forced in`l so that an effective .opening of the raw material from the inside takes place.

24. A method of impregnating raw material and fibres, characterized by the feature. that before the raw material enters the pre-digester, first moist SO: is supplied t0 it and after it has digester, a thin gas liquor is supplied which in the pores ofthe raw material -combines with the gaseous S02 which has been forced in sothat an effective opening of the raw material from the inside takes place; and after the impregnation, and before the beginning of the digestion, the last circulation liquor which is saturated with dissolved incrustations is supplied to the raw material, which incrustations enclose the outer layers 'of lthe steamed and impregnated raw material and protect them from premature opening by steam and stronger liquor.

25. A .method of impregnating raw material. and fibres, characterized by the feature that be# fore the raw material enters the pre-digester, first moist SO2 is supplied to it and after it has swollen but still before its entry -into the pre-digester, -a thin gas liquor! is supplied which in the pores of the raw material combines with the gaseous SO2 which has been forced in soL that an effective opening of the raw material from the inside takes place; and the fibres digested in the digester, after the removal of the liquor, are saturated again in a so-called concentrated quiescent digester with "fresh,` strong gas liquor which, if necessary, is assisted with the introduction of gaseous SO2 after which the bres, after the removal of the outer liquor and after addition of fresh liquor, are digested in a. further digester, if necessary, in further digesters, or the process is repeated and finally the pulp, is completely digested with a fresh liquor in an end digester.

26. A method of bleaching cellulose in a battery of digters, -characterized'by the feature 110 that a fully digested-pulp, without interrupting its progress through the system of digesters is finally supersaturated with gaseous SO2, or with gas liquor, whereby the rawV cellulose not only. takes on a lighterl colour, but also its bleaching capability and purity are increased.

27. An apparatus for digesting cellulose and similar materials comprising a battery of digesters, devices for continuously regulating the introduction of the raw materials and of the 120 chemicals, and devices for continuously regulating the removal of the digested cellulose, the chemicals, and end liquors, the digesters forming communicating vessels in order that the raw ma# may be continuously supplied and may pass through in a continuous stream, and means for automatically regulating the overflow of pulp from the end digester consisting of an overflow sllric'e and a float' connected therewith disposed before the pulp out-flow.

28. A process for digesting cellulose and similar materials, characterized by the continuous passage of the raw material through a battery con--` sisting of one or more digesters, characterized by the feature that the liquor led away from one digester .is supplied to a preceding digester as fresh liquor, so that liquor which is very much enriched in incrustations reaches the first di f gester.'

29. A procs for digesting cellulose and similar materials, characterized by the continuous passage ofthe raw material through a battery consisting of-one or more digesters, characterized by the feature that for steaming the fresh raw material, and for commencing the digestion thereof in the upper parts above the first digester, waste steam, or exhaust steam, of quite small pressure' from an external source is used. l

30. An apparatus for continuously digesting cellulose or similar materials having several digesters arranged one above another so that the 1 mass to be treated passes progrsively and continuously from one dlgeter to another a regulating member for the liquid column in the digesters, the uppermost pre-digester or end digester reaching up to the regulating member for maintaining the liquid column in the digesters.-

31. An `apparatus for continuously digesting 1Gov 

